1. Field of the Invention
The present invention relates to a magneto-optic disk apparatus, and more in particular to data reading before erasing (referred to as "erase-after-read" hereinafter) system and data reading before writing (referred to as "write-after-read" hereinafter) system in a magneto-optic disk apparatus for recording, playing back, or erasing a data signal on a magneto-optic disk by means of a semiconductor laser.
2. Description of the Prior Art
Recently, with a growing demand for increasing the capacity and operation speed of a data memory unit, there has been paid much attention to a magneto-optic disk apparatus for recording, playing back, or erasing a data signal on a magneto-optic disk utilizing a semiconductor laser.
FIG. 9 shows a block diagram of an ordinary conventional magneto-optic disk apparatus of a magnetic field modulation type. Referring to FIG. 9, the magneto-optic disk apparatus comprises a semiconductor laser unit 1, an optical head 2, a magneto-optic disk 3 which is provided with a recording film 4, a bias magnetic field unit 5 for exerting a bias magnetic field to the recording film 4 by receiving a recording signal 13 transmitted from a CPU 14. The apparatus further comprises a binary coding circuit 9 outputting a playback signal 10 to the CPU 14, and a semiconductor laser drive circuit 11 for driving the semiconductor laser unit 1. A record/playback/erase changeover signal 12 is transmitted to the drive circuit 11 from the CPU 14.
In regard to the mutual relations and operations of the above-mentioned constituent units of the magneto-optic disk apparatus, the following describes the procedures for carrying out data recording or erasing on the magneto-optic disk 3 according to, for example, a magnetic field modulation type magneto-optic disk apparatus with reference to FIG. 9. Laser beams emitted from the semiconductor laser unit 1 are focused on the recording film 4 on the magneto-optic disk 3 through the optical head 2. The recording film 4 is designed to be magnetically orientated in a direction perpendicular to the film surface when in an unrecording mode (i.e., data erasing mode) in such a manner that the magnetization of the recording film 4 is oriented, for example, in the direction from the laser beam incident side to the recording film 4.
In the data recording mode, the CPU 14 transmits a record/playback/erase changeover signal 12 to the semiconductor laser drive circuit 11 to control the semiconductor laser unit 1 to yield such a high optical output of the laser beam that the laser beam incident portion of the recording film 4 can be maintained at a temperature not lower than the Curie point of the film member. The CPU 14 further outputs a recording signal 13 to the bias magnetic field unit 5 to modulate the bias magnetic field exerted to the recording film 4 in a direction perpendicular to the recording film surface. The bias magnetic field is so modulated depending on the recording signal 13 that the bias magnetic field is oriented in the direction from the laser beam incident side to the recording film 4 when the recording data is "0", or otherwise so modulated that the bias magnetic field is oriented in the direction from the recording film 4 to the laser beam incident side when the recording data is "1". The coercive force of the recording film 4 is reduced to zero at a temperature not lower than the Curie point, so that the recording film 4 is magnetically oriented in the direction of the current bias magnetic field exerted to the recording film 4. When the recording film 4 passes through the laser beam application position and the temperature thereof becomes lower than the Curie point, the magnetization of the magnetized recording film 4 is maintained in the direction of the currently modulated bias magnetic field thereby to complete the data recording operation.
In the data playback mode, the CPU 14 transmits a record/playback/erase changeover signal 12 to the semiconductor laser drive circuit 11 to control the semiconductor laser unit 1 to generate such a low optical output of the laser beam that the laser beam incident portion of the recording film 4 is suppressed at a temperature lower than the Curie point for maintaining the coercive force. Therefore, the current magnetization of the recording film 4 is maintained because the coercive force thereof is not reduced to zero. The polarization of the laser beam applied to the recording film 4 is rotated under application of the bias magnetic field when the laser beam is reflected on the recording film 4 due to an interaction with the magnetized recording film 4. This effect is known as "Kerr effect" in the art. Since the magnetization direction of the recording film 4 differs depending on which is selected the recording state or the unrecording state, the direction of the rotation angle of the polarization of the laser beam also differs. The different rotation amount and direction of the polarization of the laser beam is detected by means of the optical head 2 thereby to play back the recorded data signal.
In the erasing operation mode., the CPU 14 controls the recording signal 13 to be only "0" so that the bias magnetic field unit 5 continues to generate a bias magnetic field onto the recording film 4 with the same magnetic orientation as that in the unrecording mode, in other words, the recording film 4 is magnetized in such a manner that the magnetization of the recording film 4 is oriented in the direction from the laser beam incident side to the recording film 4. The other operations in the erasing operation mode are carried out in the same manner as in the recording mode.
FIG. 10 shows a schematic diagram of an ordinary conventional optical modulation type magneto-optic disk apparatus. Referring to FIG. 10, the apparatus comprises a semiconductor laser unit 101 for generating a laser beam, an optical head 102 receiving the laser beam reflected on a recording film and transmitting a magneto-optic playback signal 106 to a binary coding circuit 119 which transmits a playback signal 120 to a CPU 125. The apparatus further comprises a magneto-optic disk 103 which is provided with the recording film 104, a bias magnetic field unit 105 for exerting a bias magnetic field to the recording film 104, and a semiconductor laser drive circuit 111. The CPU 125 transmits a bias magnetic field control signal 112 to the bias magnetic field unit 105, a record/playback/erase changeover signal 113 and a recording signal 114 to the semiconductor laser drive circuit 111. The above-mentioned construction is similar to that of the apparatus in FIG. 9 except for some functions of several constituent elements.
The following describes data recording and erasing operations on the magneto-optic disk 103 according to the optical modulation method with reference to FIG. 10. Laser beams emitted from the semiconductor laser unit 101 are focused on the recording film 104 provided on the magneto-optic disk 103 through the optical head 102. The recording film 104 is magnetically oriented in a direction perpendicular to the film surface in the unrecording state. In the unrecording state, the magnetization of the recording film 104 is oriented in the direction from the laser beam incident side to the recording film 104.
In the recording operation mode, the CPU 114 transmits the bias magnetic field control signal 112 to the bias magnetic field unit 105 to generate a bias magnetic field such that the magnetization of the recording film 104 is oriented in the direction opposite to the direction in the unrecording state, in other words, oriented from the recording film to the laser beam incident side. Then the record/playback/erase changeover signal 113 and the recording signal 114 are transmitted to the semiconductor laser drive circuit 111 to modulate the laser beam output of the semiconductor laser unit 101. The modulation of the laser beam output is so effected as to change the temperature distribution of the recording film 104. When the temperature of the recording film 104 is increased not lower than the Curie point, the coercive force of the recording film 104 is reduced to zero, so that the recording film 104 is magnetically oriented in a direction of the bias magnetic field currently exerted from the bias magnetic field unit 105 to the recording film 104. When the laser beam application is completed and the temperature of the recording film 104 is made lower than the Curie point, the coercive force of the recording film 104 is recovered and the magnetic orientation of the magnetized recording film 104 is maintained in the direction of the current bias magnetic field thereby to complete the recording operation.
In the playback operation mode, the CPU 125 transmits the record/playback/erase changeover signal 113 to the semiconductor laser drive circuit 111 to control the semiconductor laser unit 101 to generate such a low laser beam output that the laser beam incident portion of the recording film 104 is suppressed at a temperature lower than the Curie point, and the suppressed laser beam is applied to the recording film 104 maintaining the coercive force. The polarization of the applied laser beam is rotated when reflected on the recording film 104 due to an interaction with the magnetized recording film 104. Since the magnetic orientation of the magnetized recording film 104 differs depending on which is selected the recording state or unrecording state, the rotation angle or direction of the polarization of the laser beam also differs. The different rotation amount and direction of the polarization of the laser beam is detected by means of the optical head 102 thereby to play back the recorded data signal.
In the data erasing mode, the CPU 125 transmits the bias magnetic field control signal 112 to the bias magnetic field unit 105 to generate a bias magnetic field such that the bias magnetic field is oriented in the same direction as in the unrecording mode, i.e., in the direction from the laser beam incident side to the recording film 104. Then the record/playback/erase changeover signal 113 is transmitted to the semiconductor laser drive circuit 111 to control the semiconductor laser unit 101 to generate such a high output laser beam that the recording film 104 is maintained at a temperature not lower than the Curie point. When the temperature of the recording film 104 is increased not lower than the Curie point, the coercive force of the recording film 104 is reduced to zero, so that the magnetization of the recording film 104 is oriented in the direction of the bias magnetic field currently exerted by the bias magnetic field unit 105, i.e., in the same direction as that in the unrecording state. When the laser beam application is completed and the temperature of the recording film 104 is made lower than the Curie point, the coercive force of the recording film 104 is recovered and the magnetization direction of the recording film 104 is maintained in the direction of the current bias magnetic field, i.e., in the same direction as in the unrecording state thereby to complete the erasing operation.
In the magneto-optic disk apparatus of both the magnetic field modulation type and the optical modulation type described above, there is a growing demand for providing the function of erase-after-read and write-after-read capable of recovering recorded data even when necessary data is faultily erased or overwritten, or in such an erroneous operation as track jumping of the unit.
The following describes the erase-after-read operation of the conventional magneto-optic disk apparatus. FIG. 11 shows a flow chart of the erase-after-read operation. Referring to FIG. 11, firstly the position of the recorded data to be erased is subject to playback thereby to read the recorded data at the step S11. Secondly at the step S12, the process enters a waiting mode in which at least one turn or rotation of the disk is effected until the laser beam is applied again to the specified position. Then a data erasing operation is carried out at the step S13. It takes about several tens seconds for the magneto-optic disk to make one turn, and the magneto-optic disk apparatus has nothing to do in almost the entire waiting period. For the above reasons, the waiting period for the magneto-optic disk to make one turn in the erase-after-read operation is a serious obstacle to an attempt of increasing the operation speed of the magneto-optic disk apparatus.
In regard to the write-after-read operation, a direct overwriting is theoretically permitted in a magnetic field modulation type, where the recording and erasing operations are the same except the control procedures for controlling the recording signal, and therefore the write-after-read and the erase-after-read are carried out in the same manner. FIG. 12 shows a flow chart of the write-after-read operation. Firstly at the step 21, the position of the recorded data to be written is subject to playback so that the recorded data is read. Secondly at the step S22, the process enters the waiting mode in which at least one turn of the disk is effected until the laser beam is applied again to the specified position. Then at the step S23, a writing operation is carried out. In the write-after-read operation, the waiting period for the magneto-optic disk to make one turn is also a serious obstacle to increasing the operation speed of the magneto-optic disk apparatus for the same reasons as in the erase-after-read operation.
As shown in FIG. 13, for giving solution of the above-mentioned problems, there is a method of carrying out write-after-read or erase-after-read operations without waiting period for the magneto-optic disk to make at least one turn by employing two semiconductor laser units of a precedent-spot semiconductor laser unit 53 and a main-spot semiconductor laser unit 51, wherein the playing back operation of the recorded signal is effected with a precedent beam spot 58 while the recording and erasing operations are carried out with a main beam spot 59.
Other than the above-mentioned method, there is a method of using a two-beam semiconductor laser unit 65 as shown in FIG. 14, or a method of dividing the forward output light of a semiconductor laser unit 66 by means of a diffraction grating 67 to produce multi-laser beam to be applied onto a recording film 61 of a magneto-optic disk 60 as shown in FIG. 15.
For instance, in the aforesaid conventional magneto-optic disk apparatus where the two semiconductor laser units, i.e., the precedent-spot semiconductor laser beam 53 and the main-spot semiconductor laser beam 51 are used as shown in FIG. 13, two independent semiconductor laser drive circuits are necessary respectively for the employed two semiconductor laser units. The above fact results in a complicated circuit and requirement of focusing the two semiconductor laser beams on the recording film 61 of the magneto-optic disk 60 concurrently without aberration, which also leads to a complicated optical system and difficulty in designing and adjustment and therefore resulting in cost increase.
Also in the method of employing the two-beam semiconductor laser unit 65 for simplification of the optical system as shown in FIG. 14, however, the method is basically not free of the above-mentioned problems of the complication of the optical system, and two semiconductor laser beam drive circuits fatally causes the same circuit problems as described above.
In the method where the forward output laser beam of the semiconductor laser unit 66 is divided through the diffraction grating 67 into multi-laser beams to be applied onto the recording film 61 of the magneto-optic disk 60 as shown in FIG. 15, only one semiconductor laser unit is employed to permit provision of one semiconductor laser drive circuit giving solution to the circuit problems, however, the optical system has the same problems as in the aforesaid two examples.